The portion of illuminating light emitted from a light source, which would otherwise illuminate an ineffective area outside the display range of a liquid crystal panel may be reflected at a reflector plate in order to ensure efficient utilization of the illuminating light at an image display device known in the related art (see, for instance, patent reference 1).
In addition, projectors in the related art split light originating from a light source into two polarized light beams perpendicular to each other via a polarization splitter and use only one of the polarized light beams for projection (see, for instance, patent reference 2). In this case, only half of the light initially emitted from the light source is used for projection, and accordingly, illumination devices attempting to improve the utilization efficiency with which the light from the light source is utilized have been proposed (see, for instance, patent reference 3).    Patent reference 1: Japanese Patent No. 3660371    Patent reference 2: Japanese Laid Open Patent Publication No. 2007-72241    Patent reference 3: Japanese Laid Open Patent Publication No. 2006-243433